Electrical contacts



United States Patent ELECTRICAL CONTACTS Childress B. Gwyn, Jr., NorthAttleboro, Mass, assignor to Metals & Controls Corporation, Attleboro,Mass, a corporation of Massachusetts No Drawing. Application September21, 1956, Serial No. 611,364

9 Claims. (Cl. 200-166) This invention relates to electrical contacts,and more particularly, to electrical devices including pairs ofcooperating contacts formed of improved compositions.

In direct current applications, and particularly such applications wherevibratory inductive load characteristics (such as those encountered inautomobile-type voltage regulators) exist, transfer or migration ofmetal between a contact of a given polarity and a cooperating contact ofopposite polarity often has deleterious effects. One of thesedeleterious effects is that the surface of one of the pair ofcooperating contacts or contact elements becomes built-up, with aresulting change in the effective height of the built-up contactelement. In a precision instrument such as an automobile voltageregulator, such a change in the effective height of one of the contactelements may seriously impair the operating characteristics of thevoltage regulator whereby its operational-life is substantiallyshortened.

Accordingly, an object of this invention is to provide electrical meansembodying pairs of cooperating electrical contact elements which have acomparatively long operating life.

A further object of this invention is to provide improved electricalmeans comprising a pair of cooperating contact elements wherebydeleterious effects due to metal transfer or migration between thesecontact elements are counteracted.

A further object of this invention is to provide electrical meansincluding an improved pair of cooperating contact elements wherebybuild-up on the surface of either of these contact elements is preventedor substantially lessened.

A further object of this invention is to provide electrical meansincorporating a pair of cooperating electrical contact elements wherebycontact-surface resistance rise is inhibited and self-life failure isminimized.

A further object of this invention is to provide electrical meanscomprising a pair of cooperating electrical contact elements whichduring operation thereof inherently effect a surface fritting actionagainst each other thereby tending to obviate localized hot spots at thecooperating surfaces of the respective contact elements.

A further object of this invention is to provide electrical meansembodying a pair of cooperating electrical contact elements of oppositepolarities and formed of respective compositions whereby the electricalmeans exhibits improved operatingcharacteristics.

Other objects will be in part obvious and in part pointed outhereinafter.

The invention accordingly comprises the elements, combinations ofelements, features of construction, arrangements of parts, theingredients, combinations of ingredicuts, the proportions thereof, andfeatures of composition which will be exemplified in the structures andproducts hereinafter described, and the scope of the application ofwhich will be indicated in the following claims.

The alloys of which the respective contact elements of the cpoperatingpairs of. contactelements .of

this invention are formed are particularly useful for the voltagelimiting contacts of automobile-type voltage regulators. However, forsuch regulators, contact compositions which provide good performancecharacteristics when used as voltage limiting contacts usually alsoprovide reasonably good performance characteristics when used as currentlimiting contacts. The same holds true of the improved compositions setforth herein. Furtherfore, while the particular compositions of thisinvention are primarily suited for direct current applications, theyalso perform highly satisfactorily in alternating current applicationswhere the current through the contact element combination is in therange of 5 amperes or less, and more particularly in the range of from afew milliamperes to one ampere.

In an electrical device for making and breaking an inductive, directcurrent, electrical circuit, and incorporating the improved contactelements of this invention, the contact element of positive polarity forthe voltage limiting pair of contact elements is formed of an alloyconsisting essentially of 50% to by weight of gold and the remaindersilver. The contact element of negative polarity of the pair of voltagelimiting contact elements of this invention is formed of an alloyconsisting essentially of 60% to 80% by weight of palladium, 0.5% tol..8% by weight of a modifying agent, and the remainder silver.

The modifying agent referred to herein has a hardening effect on theresulting alloy. Furthermore, this modifying agent acts as amigration-controlling agent having the effect (when a negative contactelement of this invention is disposed in cooperating relationship with apositive contact element of this invention) of tending to reverse thedirection of metal transfer or migration which, in electrical circuitsusing direct current, ordinarily takes place from the negative contactelement to the positive contact element. The result is that, althoughmetal transfer or migration of metal from one of the contacts to theother does occur to some extent, this metal transfer or migration sooccurs (when a contact element combination of this invention is disposedin an inductive direct current circuit as described above) that theaverage or overall metal transfer or migration is substantially zero. Inthis regard, metal transfer normally occurs from the positive to thenegative contact element of the combination of this invention throughoutthe regulator vibrational frequency range of from approximately 45cycles per second to zero cycles per second. From approximately 45cycles per second to approximately 80 cycles per second the metaltransfer may go in either of the two directions between the positive andthe negative contact element; and, above approximately 80 cycles persecond, the metal transfer normally goes from the negative to thepositive contact element. Since the vibrational frequency in anautomobile-type voltage regulator generally varies from 0 to cycles persecond during its normal use, the total metal transfer or migrationamounts to substantially zero When the combinations of this inventionareused for such installations.

Also, with cooperating contact elements of a combination according tothis invention, a surface fritting action occurs at the respectivemutually engageable and disengageable surfaces of the contact elementswhereby localized hot spots at these contact element surfaces areminimized. This, in turn, has a minimizing effect on the tendency formetal transfer or migration.

Best results have been effected when the modifying agent referred toabove consisted essentially of nickel.

. Substantially identically good results have been obtained when themodifying agent consisted of a mixture of nickel and copper. In fact,unexpectedly good results are obtained by using as the modifying agentany one of nickel, cobalt, and copper and mixtures thereof, insubstantially. this same proportion of 0.5 to 1.8% by weight,

Stated otherwise, so long as the modifying agent is in the proportion offrom 0.5% to 1.8% by weight of the resulting alloy and is selected fromthe group consisting of nickel, cobalt and copper and mixtures thereof,the resulting composition is imbued with the migration-controlled andhardened characteristics which are discussed above.

A preferred example of a combination of contact elements of thisinvention is as follows: The contact element of negative purity isformed of an alloy consisting essentially of 72% by weight of palladium,1.8% by weight of nickel and the remainder silver; and the contactelement of positive polarity is formed of an alloy consistingessentially of 70% by weight of gold and the remainder silver. Asanother specific example of the respective contact element combinationsfalling Within the scope of this invention, the negative contact elementis formed of an alloy consisting essentially of 65% by weight ofpalladium, 0.5% by weight of nickel and the remainder silver; and thecontact element of positive polarity cooperating therewith being formedof an alloy consisting essentially of 60% by weight of gold and theremainder silver. As another preferred example of a contact elementcombination of this invention, the negative contact element is formed ofan alloy consisting essentially of 72% by Weight of palladium, 0.4% byweight of nickel, 1.4% by weight of copper (the nickel and coppertogether making up the modifying agent), and the remainder silver; andthe positive contact element is formed of an alloy consistingessentially of 70% by weight of gold and the remainder silver.

The efiicacy of the contact element compositions in the combinations ofthis invention is illustrated by the results of a series of life testsconducted under extremely severe operating conditions pointed out asfollows. In particular, five contact element combinations formed ofalloys presently in use in commercially-obtainable voltage regulatorswere compared with the contact element combinations formed of theimproved alloys set forth herein. Each of these contact elementcombinations was placed in a 12 volt, Type No. 1119001, Delco Remyvoltage regulator and each of these voltage regulators was disposed inelectrically operative relationship with a partially-discharged, 12-voltstorage battery and with a generator driven at a speed constantlyvarying from 1100 R. P. M. to 7000 R. P. M. and back to 1100 R. P. M.

The five presently-used contact element combinations referred to aboveappear as the first five combinations listed in the table below. Thelast two are combinations of this invention. All of the percentageslisted below are by weight.

Voltage Limiting Contact Element Combination Average Life in OperationalHours Positive Polarity Negative Polarity 89% platinum, 11% 100%tungsten l, 100

ruthenium.

72% palladium, 1.8% -.do 1. 1,250

nickel, remainder silver 64% platinum, 25% do 1,000

palladium, 11% ruthenium.

77% silver, 22.7% cad- 3% palladium, 97% 700 mium, 0.3% nickel. silver.

95% silver, 5% manga- 99.5% silver, 0.5% 718 nese. car on.

70% gold, remainder 72% palladium, 1.8% 2,050

silver. nickel, remainder silver.

60% gold, remainder 65% palladium, 0.5% 1,765

silver. niickcl, remainder s ver.

Thus, the above-named preferred contact element combination (listedsixth, above) of this invention had an average operational-life ofalmost three times the length of one of the contact element combinationspresently in use inautornotive type voltage regulators and approached anaverage operational-life of almost twice the length of that of thecontact element combination presently used which had the longest averageoperational-life.

In the above-cited tests, operational failure occurred either asirregular action by the cooperating contacts of the particularcombination which would have rendered the contacts unsuitable for theirintended purpose, or as a closed circuit whereby the cooperatingcontacts of the particular combination remained mutually engaged witheach other, either by sticking or by excessive build-up.

Each of the respective alloys forming the contact elements of thecombinations of this invention can be formed by conventional meltingprocesses.

The contact elements of this invention may constitute electricalcontacts or merely the portions of electrical contacts which engage anddisengage respectively cooperating contacts for making and breaking anelectrical current.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

I claim:

1. A pair of cooperating electrical contact elements, one of saidcontact elements comprising an alloy consisting of 60% to by weight ofpalladium, 0.5% to 1.8% by weight of a modifying agent selected from thegroup consisting of nickel, cobalt and copper and mixtures thereof, andthe remainder silver; and the other of said contact elements comprisingan alloy consisting essentially of 50% to 80% by weight of gold and theremaindersilver.

2. A pair of cooperating electrical contact elements, one of saidcontact elements comprising an alloy consisting of 60% to 80% by weightof palladium, 0.5% to 1.8% by weight of nickel and the remainder silver;and the other of said contact elements comprising an alloy consistingessentially of 50% to 80% by weight of gold and the remainder silver.

3. A pair of cooperating electrical contact elements, one of saidcontact elements comprising an alloy consisting of 60% to 80% by weightof palladium, 0.5% to 1.8% by weight of cobalt and the remainder silver;and the other of said contact elements comprising an alloy consistingessentially of 50% to 80% by weight of gold and the remainder silver.

4. A pair of cooperating electrical contact elements, one of saidcontact elements comprising an alloy consisting of 60% to 80% by weightof palladium, 0.5% to 1.8% by weight of copper and the remainder silver;and the other of said contact elements comprising an alloy consistingessentially of 50% to 80% by weight of gold and the remainder silver.

5. A pair of cooperating electrical contact elements, one of saidcontact elements comprising an alloy consisting of 72% by weight ofpalladium, 1.8% by weight of nickel, and the remainder silver; and theother of said contact elements comprising an alloy consistingessentially of 70% by weight of gold and the remainder silver.

6. A pair of cooperating electrical contact elements, one of saidcontact elements comprising an alloy consisting of 72% by weight ofpalladium, 0.4% by weight of nickel, 1.4% by weight of copper, and theremainder silver; and the other of said contact elements comprising analloy consisting essentially of 70% by weight of gold and the remaindersilver.

7. In an electrical device for making and breaking an inductive, directcurrent, electrical circuit; a first electrical contact element ofnegative polarity, said first contact element comprising an alloyconsisting essentially of 60% to 80% by weight of palladium, 0.5% to1.8% by weight of a modifying agent selected from the group consistingof nickel, cobalt and copper and mixtures thereof, and the remaindersilver; and a second electrical contact element of positive polarity,said second electrical contact element .comprising .an alloy consisting.,essentially of 50% to 80% by weight of gold and the remainder silver;said contact elements being cooperable to make and break said circuit.

8. In an electrical device for making and breaking an inductive, directcurrent, electrical circuit; a first electrical contact element ofnegative polarity, said first contact element comprising an alloyconsisting essentially of 72% by weight of palladium, 1.8% by weight ofnickel, and the remainder silver; and a second electrical contactelement of positive polarity, said second electrical contact elementcomprising an alloy consisting essentially of 70% by Weight of gold andthe remainder silver; said contact elements being cooperable to make andbreak said circuit.

9. In an electrical device for making and breaking an inductive, directcurrent, electrical circuit; a first electrical contact element ofnegative polarity, said first contact element comprising an alloyconsisting essentially of 72% by weight of palladium, 0.4% by weight ofnickel, 1.4% by weight of copper, and the remainder silver; and a secondelectrical contact element of positive polarity, said second electricalcontact element comprising an alloy consisting essentially of 70% byweight of gold and the remainder silver; said contact elements beingcooperable to make and break said circuit.

References Cited in the file of this patent UNITED STATES PATENTS2,048,647 Feussner et al. July 21, 1936 2,151,905 Emmert Mar. 28, 19392,300,286 Gwyn Oct. 27, 1942

1. A PAIR OF COOPERATING ELECTRICAL CONTACT ELEMENTS, ONE OF SAIDCONTACT ELEMENTS COMPRISING AN ALLOY CONSISTING OF 60% TO 80% BY WEIGHTOF PALLADIUM 0.5% TO 1.8% BY WEIGHT OF A MODIFYING AGENT SELECTED FROMTHE GROUP CONSISTING OF NICKEL COBALT AND COPPER AND MIXTURES THEREOF,AND THE REMAINDER SILVER; AND THE OTHER OF SAID CONTACT ELEMENTSCOMPRISING AN ALLOY CONSISTING ESSENTIALLY OF 50% TO 80% BY WEIGHT OFGOLD AND THE REMAINDER SILVER.